I have an issue with my Powertech 8KW generator not always producing power. It will produce about 3 volts instead of 120 volts. It usually has to be stopped and started several times before it produces power. It is not the transfer switch as I measure 3 volts right at the generator. Any ideas? I've asked before and unfortunately none of the answers really helped. The generator has about 700 hours on it.

One Powertech tech said to reseat the connections to the power regulator. I called again after that and another technician said that reseating wouldn't help and the brushes were probably an issue. Anyone know how I verify if the brushes are an issue? It appears I have to basically remove the entire cabinet to get to the brushes.

Hi Belfert,I don't have a Powertech but I do have a Martin gen set.Last summer while on the road ( 100 deg in TX ) mine started doing the same thing : making low voltage.Some times it was 5 volts and other times it was 30 votes.The problem was the voltage regulator. Put in a new one and set the controls and no problem since. On a Martin the voltage reg does a few things other than just hold the voltage steady. About $200 to Martin and I'm in business again.BIG tip for you : the engine will keep itself cool thru the radiator BUT you have to have LOTS of air circulating in the cabinet to cool the generator and the voltage regulator.Do what you can to move lots of air thru.Frank

The regulator is mounted in a spot where air doesn't normally circulate at all. Powertech kinda put a separate box on top of the main box and put all the controls in there. I wouldn't mind replacing the regulator as long as I knew it was bad and I wasn't just throwing parts at it.

Heat might be an issue here. It first acted up when it was about 108 degrees outside. We had to shut down the generator for a few minutes to rewire something and the generator would not put out power upon restart. I played around with things for a while and it finally started working again. It is only 80 degrees out right now so I suspect it will work just fine at this point. I might try heating things up with my heat gun a little bit to see what happens then.

The voltage regulator regulates the AC power it has nothing to do with the DC current going to the exciter fields on a Powertech that comes from the rectifier as with all DC systems probably a bad ground wire

I would flash the generator first and work from there if the exciter fields don't get enough 12 v low AC volts are what you get,

I did a little bit of research on flashing the field and it doesn't appear it is something one should do unless as a last resort on a completely dead generator. The need to flash a generator is often because it hasn't been used for a long time.

Would flashing the generator still be indicated even if the generator is running in the morning and doesn't run later that day? I've always been able to get power by shutting the generator down and then restarting it a few times. It sounds like I might be just as well off having a professional take a look at it instead of me spending the whole summer chasing after an intermittent problem. I'd prefer not to spend the money on a professional, but I can't fix everything.

I went out and started up the generator and it produced power just like it should. I ended up running it for about an hour under load. The generator has not acted up since last fall. The only thing I did during that time is to re-seat the terminals on the voltage regulator. None of the terminals seemed loose that I recall.

I'm kinda stumped right now. I suppose I should take the enclosure off and check the brushes, but I first have to figure out how to do that.

Go online at their website and see if you can get a maint manual with troubleshooting in it. I did this for my Westerbeke and found my problem to be a shorted field coil.

The manual gives a very easy to follow, step by step troubleshooting guide which will at least narrow down your problem.

I thought at first it was a dead rectifier, don't know if yours has a separate rectifier like mine or it is built into the control box. These little rectifiers are prone to failure, their function is to provide low voltage DC field current.

Anyway, the troubleshooting section enabled me to boil it down to the field which appears to have a short. Mine is '82 vintage and was on a boat so some corrosion in afield coil is no surprise.

Having said all that, my guess is it was just heat soaked. After being overheated most gensets take up to half an hour before they can be restarted. The post about high air flow over all the genset is wisdom to heed, there is no such thing as too much airflow in really hot weather.

I'm no expert on gensets but having gone through four in two buses I'm getting there!! I still have two and the one that works is in the bus. I'm in the process of reawakening the other.

I've been through most of the troubleshooting procedures in the manual and nothing has come from it. If this was a constant problem it would probably be an easy fix. The frustrating part is that it is intermittent and hasn't happened since last fall.

The problem is it will probably act up when I'm in the middle of nowhere on a weekend when I can't get technical support or any parts.

You have an exitation problem which is intermittant. If there's enough wiring, solder new spade connections on the VR leads and read them with a quality VOM. You should be reading the resistance of the rotor.

If you don't have a Powertech manual for your unit you should get one post haste. We're all prettygood mechanics but don't always understand what the guys who engineered these things are trying to tell us.

Best of luck,

NCbob

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I had to give up working on the generator tonight after only an hour or so as the skeeters are getting thick. Many thanks to those who provided help so far.

It looks like the entire generator head has to come out to replace the brushes or to do anything with the head. I am not going to do anything more with uncovering the head until someone says I absolutely need to get into the head.

3 volts output is normal residual output, which means the field is getting nothing from the rectifier because it is bad or the VR is bad since it regulates the field voltage. (Residual means that the only field strength is from the magnetism remaining in the field iron and it is getting nothing from the rectifier.) In other words it is a only a weak permanent magnet instead of the strong electromagnet it normally is when provided with DC voltage.

So, what I am saying is, since your genset is so new, I think you have a field problem and not a rotor problem. Since it is intermittent I suspect a loose connection at the rectifier, the VR or in the field wiring. It could be a shorted out field coil which is exactly the problem I have with my Westerbeke right now! It has the same weak output as yours but it is not intermittent, it is steady.

Rotor resistance is checked at the brush rings on the rotor, usually three or four rings, and the rotor shaft, but the brushes may have to be lifted off the rings. Your manual should cover this.

It could be worn brushes, but I doubt it since it is so new. On the other hand, it is not unusual to find a broken brush since they are so brittle.

Unless the PT is a really different animal the rectifier provides DC to the field and the VR controls that DC voltage. It could get DC directly from a battery but have never seen one that does. Have never seen a VR that controls at the AC output although it senses the AC output to tell the VR what to do?

If there is anything connected to the output it will mess up any ohm readings so they will need to be disconnected for accuracy.

If you open it and have a look you may be able to see any shorted or disconnected wires.

OR, it may just be a loose connection at the genset controller. These things vibrate a lot and loose connections and broken wires are not all that unusual.

Without knowing more I would hesitate to even open up the head, especially since it is working well now!! I definitely would not do any soldering to rotor wires.

This is really frustrating, it took me half an hour to type this because the page keeps locking up, bummer!

I talked to Powertech service this morning and they suspect the brushes are sticking. The only way to get at the brushes is to open the end of the head. I spent this evening unbolting the generator and moving it so I could pull the panel off that covers the end of the head. It is unclear how the end of the head comes off. It is getting late so I decided to call Powertech tomorrow morning.

I would not be surprised if the brushes are sticky based on the amount of dust and dirt in and around the generator. I need to do a better job cleaning out the dust and dirt after going out to the desert each fall.

An even bigger pain is the fact I have to unbolt the generator mounts and then raise everything up an inch or two to get to all the bolts to remove the end of the head. I could really use an engine hoist, but I don't have one. I guess I better get to work.

I used pry bars and thin boards to lift mine. There is a lip on the outside edge I had to slide it over. I have a hoist but a hoist requires way too much overhead space even to hook it up, never mind lifting it.

I used a come-along and nearby tree to slide it out. Helps if you live in the boonies with lots of trees! I slid it onto a 1000 lb capacity flatbed wagon I got from Harbor Freight and hauled it away.

I also considered splitting the head cover before re-installing it so it could come off in two pieces. I may do this yet if I re-install it but for now I'm going with the little Honda and using the diesel for a house backup.

If your rectifier is inside the head like mine you may want to do this. Yours probably is inside the controller box, a much better place for it.

My 10kw Powertech is brushless. I guess the smaller gensets have exciter brushes. My genset is in a very tight compartment-so small the radiator is remote mounted with a 1/2 hp 2spd squirrel cage blower. To ventilate the gen compartment, I use from grainger an 8" inline bathroom ventilator (it can take moisture) that puts out 250 cfm. The fan blows directly on the alternator end so to get the coolest air. I have loaded up the genset and after an hour, I can still put my hand on the alternator head because of the good ventilation. Keeping it cool is important. Good Luck, TomC

After mulling it over some more I realized the best course of action would be to pull the entire unit out. The problem is I can't lift from the bottom of the generator head or the bottom of the engine. I need to lift from the top and I'm not sure I have enough room for an engine hoist.

I called my buddy who originally installed the generator with his forklift and he is going to stop by on his way from work tomorrow to look at it. I suspect we'll end up taking the bus over to his house to lift the generator out with the forklift and then use the forklift to lift the engine up so the generator end is clear to take the end cap off. The generator is all disconnected except the fuel lines so we can have it out in 10 minutes or so.

My 7.7 diesel Westerbeke is excited by the rectifier which depends on a small AC voltage to excite the field. I presume residual magnetism is what gets the whole chain started and the reason they sometimes have to be flashed since this mostly restores the residual magnetism plus ensures the correct polarity.

AC output is taken directly from the brush rings on the rotor.

As I remember, one of the diagnostic tests is to apply 12V DC directly to the field, bypassing the rectifier, and this produces around 70 V AC if the field is OK. Don't hold me to this because it is from memory of the stuff I did two months ago!

Success! My friend who repairs forklifts for a living came over and looked at the generator this evening. He works on a lot of large electric motors in his line of work. He determined that just the wire mesh could come off and we could get to the brushes that way. No need to pull the end of the head which would require lifting the motor up.

The Powertech tech was right and the brushes are sticky. One brush is worn way shorter than the other one and it was stuck. I'm surprised the generator made power at all. A new set of brushes and I should be on to the next repair.

However, I go along with the other guys - it isn't over till it's over!!

You also need to check the rotor ring for the one brush worn more than the others, it may be faulty or, at the least, have a rough spot that needs to be smoothed. Brushes usually last for years and years.

Does it have four rings?

Keep the old brush assembly for spare parts. Unless these are really odd-balls replacements are usually easy to find at any electrical supply business. Manufacturers don't usually try to reinvent common parts even though they often use their own part numbers and charge triple the original price!

I talked with Tony at Reliance Electric Motor Repair. I gave him all the numbers from my Marathon head and he contacted them. It turns out the brush assembly is an obsolete item from Marathon even though the head is only six years old. I drove out to Hudson this past week and Tony put new brushes in the existing holder for less than $15. (Powertech apparently has new brush holders still in stock, but not cheap.)

The new brushes are back in the generator as of this past weekend and it is making power again. I'm hoping this fixes my intermittent problem of no power from time to time.

Wish mine had been that simple, I've had two dead gen heads in the past year. Never did know what was wrong with the last one and the latest one has a shorted field. However, I plan to repair this one one way or another because it is a very stout genset.

My theory on brushes is there is always something available, the hard part is identifying the brush. I consider brushes pretty much generic like bolts and nuts but a bit more specific.